JP2010539334A - Current controller for feeding network of electrochemical coating equipment - Google Patents

Abstract

A power control device for an electrochemical coating facility that is as cost-effective as possible and that guarantees as efficient and reliable operation of the coating facility as well as high coating quality is provided.
In a current control device (1) of a feeding network (2) comprising a number of anodes (5) and a number of cathodes (3) in an electrochemical coating facility, the current control devices (1) are controlled independently of each other. A number of possible control modules (6), each control module (6) being a function of position and time between one anode (5) and one cathode (3) of the feed network (2) Is configured to form and control a local current of the magnitude set as.
[Selection] Figure 1

Description

  The present invention relates to a current control device for a feeding network of an electrochemical coating facility.

  In an electrochemical coating facility, the condensation of the coating material on the workpiece indirectly between the workpiece to be coated and the medium in which the coating material is dissolved and / or between the medium and the external electrical conductor. Therefore, the object to be processed is thinly or locally covered with the material layer. In addition to changing the aggregation state of the coating material, the coating material may be chemically changed during the condensation process on the workpiece. The medium may be in an aggregate of liquid, gas or plasma and may be the coating material itself or a solvent or transport medium containing the coating material.

  Known electrochemical coating methods include, for example, plasma coating methods. In the plasma coating method, a highly diluted gas is generally ionized by high electric field excitation, and thereby changed into a plasma aggregation state. Due to the chemical reaction in the plasma, the reaction products are deposited on the substrate, in particular the workpiece to be coated (sputtering). Electrolytic coating methods belong to another important subgroup of electrochemical coating methods. In the case of the electrolytic coating method, ion diffusion is induced in an electrically dissociable medium by an externally applied electric potential, and this medium is indirectly used as a material for a workpiece to be carried into the medium. Precipitation occurs. In this way, the metal coating is applied to the object to be processed by electrolyzing the melt or solution of the metal salt, for example, by electroplating. In this case, an object to be processed, which is generally a metal, is conductively connected to one electrode, particularly the cathode, and an external potential is applied between the electrode and the other electrode corresponding to the electrode, particularly the anode. A positively charged metal ion (cation) in the molten metal salt or solution is electrically neutralized upon contact with the object to be treated, and is deposited on the object as metal atoms. A coating process in which the workpiece is brought into a mostly liquid medium for coating purposes is known as a dip coating process.

  In the case of dip coating by electrolysis, the layer formation per unit time on the coated workpiece is a function of many parameters, in particular the applied potential, time as well as the material layer already formed on the workpiece. Is included. On the other hand, in the coating process at a constant potential, the ion concentration in the medium decreases with time. In contrast to this, even when the chemical properties of the immersion bath, in particular when the ion concentration is kept constant, the current intensity of the ion stream moving towards the cathode is reduced, resulting in a decrease in layer formation per unit time. . This effect is amplified when the already formed material layer has an insulating property, which again depends on the conductivity of the cathode material, the time-dependent conductivity of the medium with ions, the conductivity of the layer material. And depending on the ratio of these electrical conductivities. When considering all the influence parameters, the layer formation per unit time generally decreases under a constant potential as a whole. The potential must be increased continuously over time.

  In industrial dip coating equipment configured for coating large workpieces, for example for the coating of automobile bodies, there is generally some constant for technical reasons due to the DC voltage that feeds the dip bath. An output unit that can only be adjusted to this potential value is used. These potential values are also called voltage levels. In addition, switching between immersion bath voltage levels during the coating process causes disadvantageous discontinuities in layer formation, especially when there is a short current spike when switching to the next higher voltage level. This adversely affects the coating quality. This voltage level or each voltage level is generated by rectifying and smoothing the AC voltage from the AC voltage supplied from the outside by the system / circuit components. Especially for cost reasons, a low rectified pulse number circuit is used. A circuit with a low rectifying pulse number is clearly lower in cost than a circuit with a high rectifying pulse number and requires relatively little regulator cost, but it causes a high reactive power component in the external power system. Therefore, a burden is imposed on the power supply system, and the operating cost of the coating equipment increases. Further, in order to prevent production interruption caused by the failure of the output unit, at least one spare unit connected to an external power supply system is generally installed through another system / circuit component. However, such redundant components that are not normally required further increase the cost of the coating equipment.

  The object of the present invention is to provide a power control device for an electrochemical coating facility that is as cost-effective as possible, ensures the most efficient and reliable operation of the coating facility, and ensures a high coating quality. There is.

  The object of the present invention is solved by the features of claim 1. According to the present invention, in a current control device for a feeding network including a number of anodes and a number of cathodes in an electrochemical coating facility, the current control device has a number of control modules, and each control module is one of the feeding circuit networks. It is configured to form and control a local current of a magnitude set as a function of position and time between the anode and one cathode.

  Commonly used dip coating equipment for automobile bodies usually has 2 to 4 output units. The first unit supplies a predetermined DC voltage to the immersion bath. During the coating process, the current intensity in the immersion bath decreases, and the layer formation thickness per unit time decreases accordingly. At a given point in time, the second output unit supplying the elevated voltage to the immersion bath is turned on, so that the layer formation thickness per unit time rises again, so that the time average is a constant given in advance. Corresponds to the value. The current and voltage applied to the immersion bath are subject to overall boundary conditions that limit the continuous tunability of the potential applied to the immersion bath and thus limit the voltage levels described above. Thus, for example, there are target values to be achieved in order to ensure effective layer formation, while on the other hand there are limit values that must not be exceeded in order to prevent local partial discharges from occurring in the coating object. However, in order to guarantee a high coating quality, it is important that the layer formation be as constant as possible per unit time at any point in time. Furthermore, the spatial distribution of the layer thickness on the surface to be coated can only be controlled to a limited extent, which is disadvantageous especially when trying to aim at spatially variable layer formation.

  Since both output units are powered by an AC voltage from an external system, a power converter circuit having a rectifier that converts the AC voltage / AC current into a pulsating DC voltage or a pulsating DC current is provided. With the buffer capacitor and the buffer inductance, the voltage or current is smoothed by reducing and compensating the fluctuation amplitude.

  The corresponding boundary conditions on the system side regarding the voltage and current in the immersion bath are the boundary conditions regarding their amplitudes and their relative phase differences in the alternating voltage and alternating current. In particular, for the phase difference between the alternating voltage and the alternating current in the power converter, the minimum value determined by the voltage level in the immersion bath is given in advance. However, a so-called phase difference reactive power that can be reduced only to a predetermined value corresponding to the minimum value of the phase difference is generated in the system.

  Furthermore, power converter circuits with a low rectifying pulse number are usually used for cost reasons, and the power converter circuit with a low rectifying pulse number is a high-frequency harmonic component of the AC voltage and AC current at the time of load, so-called harmonics. In the wave, an overall greater amplitude burden is created in the power supply system than a power converter circuit with a high number of rectified pulses. These harmonic burdens cause additional reactive power on the power system side.

  The present invention thus starts from the idea of modularizing the current control for the feeding network that feeds the immersion bath. The lack of feasibility of forming a uniform layer on the object to be coated and the lack of possibility of reducing reactive power generated in the external power supply system during bath current supply are largely due to the small number of output units. It can be considered that this is due to the generation of a large overall bath current. The number of variable parameters is considerably smaller in the defined boundary conditions. Apart from this, with the help of a very large number of separate and individually controllable output and control modules, a local current is created between each cathode and each anode in the bath. Can be controlled. In this way, layering per unit time at various levels can be realized with targeted control, especially in the defined spatial region of the bath, so that, for example, in the case of an automobile body, the roof of the vehicle during the coating process. The B pillar can be thickly coated. Equilibrium effects within the bath that attempt to equalize the spatially and temporally defined distribution of the current field within the bath can be avoided or reduced by circuit engineering measures and appropriate network topology.

  The currents controlled by the individual control modules are subject to boundary conditions that are not the same as the overall bath current, so in particular the AC voltage and AC amplitudes applied to the system side of the control module and their AC The relative phase difference between the voltage and the alternating current can be reduced. As a result, the phase difference reactive power in the system decreases as a whole. Furthermore, since the harmonic components of the AC voltage and the AC current generated by the individual control modules are not statistically dependent on each other, the power supply system, which is considered to be caused by the harmonic action due to the statistical interference of the waves The amount of total reactive power is clearly reduced.

  Furthermore, a relatively large number of control modules eliminates the need for a large number of additional modules as spare modules. The system already has a high redundancy, so a failure of one control module during the coating process does not cause an essential process disturbance. Furthermore, individual control modules or modules can be selectively turned on or off during the coating.

  The idea that has been discussed so far, which is the starting point of the present invention, can be transferred to the generalized case where the immersion bath is replaced by the medium of any kind of electrochemical coating equipment.

  In an advantageous embodiment of the current control device, one control module or each control module comprises a circuit arrangement with a plurality of power converters, in particular a plurality of rectifiers. The rectifier converts alternating current from an external power supply system into direct current supplied to the bath. A high number of rectified pulses can be obtained by means of a unified and repeatedly expandable circuit arrangement of several rectifiers, in particular a circuit arrangement connected in parallel, so that the harmonic components of such a circuit can be repeated in a corresponding manner. Reduced to The number of rectification pulses is the number of voltage waves or current waves of the same period generated in one fundamental wave period, and the relative phase difference between two partial waves before and after two phases divides the period by the number of rectification pulses. Given by.

  One power converter or each power converter may be connected to a plurality of anodes or cathodes of the feeding network. In the case of a coating facility by electrolysis for metal coating, each coating object may be conductively connected to one cathode, and the one power converter or the combination of each power converter may be performed on the anode side.

  One circuit device or each circuit device of the power converter may comprise a series circuit of a controllable rectifier and a non-control rectifier. The basis of this local circuit connection form is the so-called buck-boost connection principle, which optimizes the phase difference between AC voltage and AC current during load operation on the system side. Accordingly, a correspondingly small phase difference reactive power is realized.

  In an advantageous development of the circuit arrangement of the power converter, one controllable rectifier or each controllable rectifier is realized as a thyristor bridge and / or one non-control rectifier or each non-control rectifier as a diode bridge. This type of combination has the advantage that an uncontrolled diode bridge is much more cost effective than a controllable power converter.

  The current control device is preferably configured such that one control module or each control module is connected to a plurality of isolation transformers.

  In a particularly advantageous configuration of the current control device, one controllable rectifier or each controllable rectifier is connected to each one isolation transformer, and one non-control rectifier or each non-control rectifier is each one other Connected to the isolation transformer.

  Such a configuration is realized, for example, in a circuit device in which a diode bridge and a controllable rectifier connected in series with each other are connected to the first or second isolation transformer. The first isolation transformer supplies the diode bridge with a first current in phase with the external AC voltage, and the second isolation transformer supplies the controllable rectifier with a 30 ° phase on the system side relative to the first current. A shifted second current is supplied. This type of rectification circuit feed of twelve rectification pulses of this rectification circuit, i.e. feed with a phase shift of 30 °, for example, uses a first isolation transformer of vector type Dy0 and a second isolation transformer of vector type Dy5, This can be realized by feeding 6 rectified pulses each having a phase shift of 60 °. Therefore, this is a comparatively cost-effective rectifier circuit with twelve rectifying pulses, and this rectifier circuit with twelve rectifying pulses has a small number of rectifying pulses, particularly six rectifying pulses, with respect to the total harmonics generated. This is advantageous compared to a rectifier circuit.

  On the other hand, when the power supply with the number of rectification pulses of 12 is already possible on the system side, these isolation transformers may be configured as the same type, for example, a vector type Dy0 isolation transformer.

  As a complement to the statistical independence of harmonic fluctuations caused by individual control modules, and thus the overall reduction of harmonic components resulting from statistically equidistant interference, the harmonic amplitude is added to the number of control modules. By reducing in inverse proportion, an additional reduction of harmonics affecting the external system is achieved.

  Overall, particularly effective reactive power reduction is achieved by reducing the phase difference reactive power. As a result, the power factor of the current control device, which represents the ratio of the active power actually used to the total power in the power supply system including the reactive power, can reach a value higher than 0.94, for example. A value higher than 0.8 can still be reached at 5% load. The reduction in reactive power particularly reduces the burden on the system transformer that supplies power.

  The rectifier circuit with 12 rectifying pulses generates twice the current and voltage maximum values on the DC current side as compared with the control with 6 rectifying pulses. The maximum amplitude is likewise small. Accordingly, the direct current and the direct voltage generated by the rectifier circuit having 12 rectifying pulses have relatively small fluctuations. For a rectifying circuit with a suitable 12 rectifying pulses, the fluctuation amplitude can be less than 1% of the generated DC current or DC voltage. Therefore, the buffer capacitance and the buffer inductance required for DC current smoothing or DC voltage smoothing realized by, for example, a smoothing capacitor or a smoothing reactor can be made smaller than in a rectifier circuit with a low number of rectification pulses, so that current control as a whole is possible. The efficiency and economic efficiency of the device is improved.

  In another advantageous configuration variant of the current control device, a decoupling circuit for decoupling each control module from the immersion bath is constructed between one control module or each control module and each a plurality of anodes. The decoupling circuit includes a plurality of series-connected diodes, each of which is connected to a respective anode in a conduction direction.

  This type of decoupling circuit provides backflow compensation so that the current field in the bath defined and set between the anode and the cathode does not collapse and / or homogenize. It is possible to prevent a balancing current between feed points adjacent to each other.

  The decoupling circuit includes a series circuit of first and second diodes, each diode is connected to the first or second anode in the conduction direction, and the first diode is controlled via the switching element and the inductance in the blocking direction The second diode may be connected to the module and connected to the first diode, the first anode, and the smoothing capacitor in the blocking direction.

  A current for both anodes flows through the first diode, and a current for the second anode flows through the second diode. Each voltage drop in the first and second diodes can result in a different voltage at the first and second anodes. This voltage difference is compensated by the inevitably long cable path for one anode on the bath.

  The installation of the smoothing capacitor between the two diodes connected in series of the decoupling circuit cannot cause an oscillation circuit between the smoothing capacitor and the inductance provided as a DC reactor, which is necessary for smoothing the entire current. Has the advantage. The smoothing capacitor is charged by the power converter circuit via its inductance and the first diode in the conduction direction. However, the reverse oscillation of the energy of the smoothing capacitor to the diode is impossible due to the blocking action of the diode. Thus, energy can only be discharged through the impedance of the bath, preventing unwanted balancing discharge processes and compensation processes in the bath. Furthermore, the braking with energy loss required for the vibration circuit is not necessary.

  For the current control device, a calculation unit having a simulation model for simulation of voltage setting and / or current setting may be provided. This simulation determines the voltage and current settings in the bath and the parameters related to them, especially for the coating process. Determination of the target coating thickness relative to the position in the CAD display of the object to be coated is used to set the voltage and / or current applied to the bath via one anode or each anode as a function of the target position in the bath. It is caused by the driving program.

FIG. 1 is a circuit diagram schematically showing a current control device. FIG. 2 is another circuit diagram schematically showing the current control device.

  Hereinafter, an embodiment of a current control device according to the present invention for a feeding network of an electrochemical coating facility will be described with reference to the drawings.

  In different drawings, portions corresponding to each other are denoted by the same reference numerals.

  FIG. 1 is a circuit diagram of a current control device 1 of a feeding network 2 of an electrochemical coating facility.

  The potential adaptation required in the coating process is taken into account by adaptation of the secondary voltage of the isolation transformer. The adaptation of the secondary voltage of the isolation transformer results in an additional optimization of the reactive power component in the operational system.

  The power supply network 2 includes a large number of cathodes 3 that are conductively connected to a large number of coating objects 4 and a large number of anodes 5 that are grouped in pairs. The anode 5 and the cathode 3 with the coating object 4 are carried into a dipping bath containing a metal salt solution.

  The current control device 1 includes a number of control modules 6 each having a controllable thyristor bridge 8 and an uncontrolled diode bridge 9. Both the thyristor bridge 8 and the diode bridge 9 are connected to one three-phase insulating transformer 10 or 11 on the AC system side. The thyristor bridge 8 is connected to the pair of anodes 5 via the decoupling circuit 12 in the conduction direction. The decoupling circuit 12 includes a first diode 13 and a second diode 14, each of which is connected to a separate anode 5 of the pair of anodes 5 in the conduction direction. The first diode 13 is connected to the thyristor bridge 8 via the switching element 15 and the DC reactor 16 in the blocking direction. The second diode 14 is connected to the first diode 13 in the blocking direction, the anode 5 connected to the diode 13 in the conduction direction, and the smoothing capacitor 17.

  The isolation transformers 10 and 11 supply alternating voltages to the thyristor bridge 8 or the diode bridge 9 respectively, and these alternating voltages are in phase or have a phase angle shifted from each other by 30 °. The series circuit 7 composed of the thyristor bridge 8 and the diode bridge 9 generates a pulsating DC voltage, and also generates a pulsating DC current from an AC current having the same frequency supplied through the isolation transformers 10 and 11. The fluctuation amplitude of the voltage or current is smoothed by the smoothing capacitor 17 or the DC reactor 16. In this case, the formation of the LC oscillation circuit composed of the DC reactor 16 and the smoothing capacitor 17 is prevented by the first diode 14 of the decoupling circuit 12 interposed in terms of circuit technology. This is because the energy stored in the electric field of the smoothing capacitor 17 does not flow back toward the DC reactor 16 as a current in the blocking direction of the first diode 14. The decoupling circuit 12 avoids the electric field balancing effect between the cathode 3 and the anode 5.

  2 shows another circuit diagram of the current control device shown in FIG. 1 with a schematic display based on FIG.

  There is a control module 6 comprising a thyristor bridge 8 and a diode bridge 9 connected to the feeder network 2 by means of an isolation transformer 10 or 11 and connected to the anode 5 on the bath side. Unlike FIG. 1, the pair of anodes 5 shown in FIG. 1 connected to each control module 6 is shown as a unitary body in this figure. The decoupling circuit 12 shown in FIG. 1 is not shown here. The area of the immersion bath 18 is indicated by a separation line 19.

  In order to achieve uniform layer formation on the automobile body passing by the anode 5 in the immersion bath 18, DC voltage and DC current of different heights are applied to the anode 5 depending on the linear position with respect to the immersion bath 18. Is done. The thyristor bridge 8 and the diode bridge 9 of the control module 6 connected to each anode 5 are supplied from the AC voltage or AC current supplied in the required magnitude by the isolation transformer 10 or 11 each time. DC voltage and current are generated. Therefore, depending on the position with respect to the immersion bath 18, the isolation transformer 10 or 11 is configured to perform a voltage difference with different heights.

  Other details of this figure correspond to the details of FIG. 1 and can be derived from FIG.

  Any number of control modules can be connected in parallel to increase the current, and the interconnections should be made according to the master / slave principle in particular. As a result, conventional systems can be reproduced in exactly the same way in the implementation of ATL (anode electrophoretic coating) and KTL (cathodic electrophoretic coating). This does not exclude the mixed operation of ATL and KTL.

  The direct current circuit comprises in particular a series circuit of non-control power converter and controllable power converter and storage elements (L and C). This application is intended to cover any order of these elements in a series circuit. For example, the order of controllable bridge, inductance, uncontrolled bridge, capacitive smoothing element, diode can be considered.

  In order to further reduce the influence of the number of rectifying pulses 12 on the system, two systems with isolation transformers that are offset by an angle of 15 ° with respect to the first system may be connected in series.

DESCRIPTION OF SYMBOLS 1 Current control apparatus, 2 Feeding network, 3 Cathode, 4 Coating object, 5 Anode, 6 Control module, 7 Series circuit, 8 Thyristor bridge, 9 Diode bridge, 10, 11 Isolation transformer, 12 Decoupling circuit, 13, 14 diode, 15 switching element, 16 DC reactor, 17 smoothing capacitor, 18 immersion bath, 19 separating line

Claims (10)

  A current control device (1) of a feeding network (2) including a plurality of anodes (5) and a plurality of cathodes (3) in an electrochemical coating facility, the current control devices (1) being controllable independently of each other Having a plurality of control modules (6), each control module (6) being set as a function of position and time between one anode (5) and one cathode (3) of the feeding network (2) A current control device configured to form and control a local current of a specified magnitude.   The current control device according to claim 1, wherein one control module (6) or each control module (6) comprises a circuit device (7) having a plurality of power converters (8, 9).   3. A power converter (8, 9) or each power converter (8, 9) is connected to a plurality of anodes (5) or cathodes (3) of a feed network (2). Current control device.   One circuit device (7) or each circuit device (7) of the power converter (8, 9) is realized as a series circuit (7) of a controllable rectifier (8) and a non-control rectifier (9). The current control device according to claim 2 or 3.   One controllable rectifier (8) or each controllable rectifier (8) is realized as a thyristor bridge (8) and / or one uncontrolled rectifier (9) or each uncontrolled rectifier (9) is a diode bridge (9) The current control device according to claim 4, which is realized as:   6. A current control device according to claim 2, wherein one control module (6) or each control module (6) is connected to a plurality of isolation transformers (10, 11).   One controllable rectifier (8) or each controllable rectifier (8) is connected to one isolation transformer (10) each, and one uncontrolled rectifier (9) or each uncontrolled rectifier (9) The current control device according to claim 5 or 6, wherein the current control device is connected to one other isolation transformer (11).   A decoupling circuit (12) including a plurality of diodes (13, 14) connected in series is formed between one control module (6) or each control module (6) and each of a plurality of anodes (5). 8. The current control device according to claim 1, wherein each diode (13, 14) is connected to one anode (5) in the conducting direction.   The decoupling circuit (12) includes a series circuit of a first diode (13) and a second diode (14), and each diode (13, 14) has a first anode (5) and / or a second in the conduction direction. The first diode (13) is connected to the control module (6) via the switching element (15) and the inductance (16) in the blocking direction, and is connected to the second anode (14). 9. The current control device according to claim 8, wherein is connected to the first diode (13), the first anode (5) and the smoothing capacitor (17) in the blocking direction.   10. The current control device according to claim 1, further comprising a calculation unit having a simulation model for simulating voltage setting and / or current setting.

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